Rocket fuse with a cocked piston

ABSTRACT

A rocket fuse including a dashpot timer in which a piston extension is adapted to hold a slider assembly in a retracted position. The slider assembly contains a detonator and also is under the influence of a spring which bears against the piston extension causing the piston to cock relative to the cylinder. A spring biased weight bears against the piston to hold it in a position at which the slider assembly is maintained in its retracted position by the piston extension. When the rocket is projected and experiences predetermined acceleration, the generated forces shift the weight away from the piston which is then adapted to travel in its cylinder. When the acceleration forces are present for a predetermined period of time and maintains the weight away from the piston, the movement of the piston in its cylinder will eventually cause the piston extension to clear the slider assembly. At this moment the slider assembly is shifted by means of its spring to a position at which the detonator is aligned with the detonator pin and the explosive train to thereby arm the fuse.

[4 1 Mar. 28, 1972 r. I Elite ttes aet reed [54] OKIKET FUSE WITH A COCKED PISTON [72] Inventor: David 8. Breed, PO. Box 349, Lake Hopatcong, NJ. 07843 [22] Filed: Apr. 1,1969

[21] Appl.No.: 811,968

[52] U.S.Cl ..102/80,58/144 [51] llnt.Cl .F42c5/00,F42c7/00,F42c15/20 [58] FieldoiSearch ..lO2/80;58/144 [56] 7 References Cited 7 V UNITED STATES PATENTS 2,441,939 5/1948 Nichols ...102/80 2,715,873 8/1955 Thompson l02/80X 2,812,714 11/1957 Wheatleyetal. ..102/8O Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas H. Webb Attorneyl(ane, Dalsimer, Kane, Sullivan and Kurucz [57] ABSTRACT A rocket fuse including a dashpot timer in which a piston extension is adapted to hold a slider assembly in a retracted position. The slider assembly contains a detonator and also is under the influence of a spring which bears against the piston extension causing the piston to cock relative to the cylinder. A spring biased weight bears against the piston to hold it in a position at which the slider assembly is maintained in its retracted position by the piston extension. When the rocket is projected and experiences predetermined acceleration. the generated forces shift the weight away from the piston which is then adapted to travel in its cylinder. When the acceleration forces are present for a predetermined period of time and maintains the weight away from the piston, the movement of the piston in its cylinder will eventually cause the piston extension to clear the slider assembly. At this moment the slider assembly is shifted by means of its spring to a position at which the detonator is aligned with the detonator pin and the explosive train to thereby arm the fuse.

6 Claims, 4 Drawing F lgures T m j ROCKET FUSE WITH A COCKED PISTON CROSS REFERENCE TO OTHER APPLICATIONS The present application relates to a timer comprising a piston which travels in a cylinder at a controlled rate due to the predictable flow of a fluid contained in the cylinder through a predetermined clearance between the piston and interior cylinder wall to occupy the ever increasing volume behind the piston. Dashpot timers of this general type are further described in U.S. Pat. No. 3,171,245 issued on Mar. 2, 1965 and the currently pending application Ser. No. 687,207 filed Dec. 1, 1967 which issued as U.S. Pat. No. 3,458,991 on Aug. 5, 1969.

BACKGROUND OF THE INVENTION In the above cited references, a dashpot timer comprising a cylindrical piston disposed within a cylinder filled with a fluid in either gaseous or liquid form, is disclosed. In order to obtain consistency and predictability in the rate of travel ofthe piston through the cylinder over several runs, it has been proposed to dispose the piston against the wall of the cylinder by various means, such as by inclining or tilting the cylinder. Also, it has been suggested that coating the surface of the piston with a polymeric material, such as Teflon, contributes to the predictability of the fluid flow rate between the piston and cylinder wall and hence the rate of descent by maintaining the piston in the center of the cylinder.

In many instances, particularly in military and aerospace applications, space limitations require that the piston of such a dashpot timer accurately travel a relatively small distance through its associated cylinder over an extended period of time and, of course, that such travel be consistently accurate over several runs and from unit to unit. Although this has been obtained to a great extent by coating the dashpot timer piston in the manner described in the pending applications so as to keep the piston substantially in the center of the cylinder, there are still many applications, particularly in connection with military ordinance devices where that solution is not preferred and/or slower piston travel rate is required. In this connection, it should be noted that maintaining the piston in the center of the cylinder increases the travel time by a factor of about 2.5 (over keeping the piston against the wall of the cylinder) whereas in accordance with the present invention factors in excess of are dramatically available.

It is, therefore, the principal object of the present invention to provide an accurate dashpot timer for use in those applications where space or other limitations are prime considerations, for insuring the consistent positioning of the piston within the cylinder and to provide such a timer which is exceptionally reliable, susceptible to long life, relatively inexpensive to manufacture, and which is accurate over a wide range of tem eratures.

SUMMARY OF THE INVENTION These and other beneficial objects and advantages are attained in accordance with the present invention by providing a dashpot timer comprising a cylinder having a substantially cylindrical interior wall with a piston disposed for movement within the cylinder and having an outer diameter slightly less than the inner diameter of the cylinder whereby to define a substantially annular orifice between the piston and cylinder. The timer is further provided with means for cocking the longitudinal axis of the piston relative to the longitudinal axis of the cylinder and for maintaining the piston in a cooked position throughout the travel of the piston through the cylinder. The motivation behind the use of a piston, the orientation of which is other than parallel to the axis of the associated cylinder is that by so doing, a circumferential flow of fluid is created within the cylinder as displaced fluids are shifted to a position behind the piston as the piston descends through the cylinder. This circumferential flow causes a slow down in the rate at which fluid is displaced and hence the rate at which the piston can descend. The circumferential flow also causes hydrodynamic forces to be built up within the cylinder which tend to align the piston and to shift it to the center of the cylinder. These hydrodynamic forces must be overcome by the cocking means which thus must remain in operative contact with the piston throughout the piston s descent.

Other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a fragmentary, side elevational, partial sectional view of a dashpot timer incorporating the teachings of the present invention;

FIG. 2 is a horizontal sectional view thereof taken along reference line 2-2 of FIG. 1 in the direction indicated by the arrows;

FIG. 3 is a graph which shows the effect on time which the piston position has as the piston is moved from side travel to cocked travel for a piston whose length to diameter ratio is 0.5, and

FIG. 4 is a cross-sectional side elevational view of a rocket fuse employing a dashpot timer ofthis invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is depicted in the accompanying drawings wherein similar components bear the same reference numeral throughout the several views. Reference is now made to FIGS. 1 and 2 wherein a dashpot timer 10 is illustrated which incorporates the teachings of the present invention. The timer 10 includes a cylinder 12 and a piston 14 slidably disposed therein. The dimensional tolerance of the cylindrical interior wall 16 of the cylinder and the cylindrical exterior wall 18 of the piston 14 provide for an annular orifice 20 through which a fluid, in gaseous form, is adapted to flow. The mating diameters represented by the respective walls 16 and 18 are very closely dimensionally controlled to provide a known clearance (in the form of orifice 20) through which a known amount of gas must pass from the beginning to end of the prescribed time interval (represented by the length of lon gitudinal travel of the piston 14 in the cylinder). In this connection, at least one ofthe cylinder ends 17 and 19 is sealed to assure fluid flow through the orifice 20. Certain applications will provide for the sealing of either or both cylinder ends. In the disclosed embodiment of FIG. 1, end 19 of cylinder 12 is closed while end 17 is open. Further, one or both of the walls 16 and 18 may be coated with a polymeric, friction resistant coating such as Teflon, as described in the pending application.

The piston, which is cylindrical in shape, extends between terminal shoulders 22 and 24. An axially aligned extension 26 of the piston extends outwardly beyond one end of the cylinder from shoulder 24 and a spring 28 is provided bearing on the extension 26 and extending transverse thereto. The spring 28 has one end 30 fixed with respect to the cylinder and the other end 32 in contact with the extension 26 thereby exerting a transverse force on the piston causing a slight rotation of the longitudinal axis of the piston relative to the cylinder axis so as to cock the piston relative to the cylinder axisv Cooking the piston in the manner described effectively increases the path that fluid displaced from in front of the piston must travel by causing the fluid to assume a circumferential path, as shown by the arrows on FIG. 1, rather than a direct longitudinal path, and hence increases the time required for the piston to travel a given longitudinal distance along the cylinder axis. This circumferential fluid flow causes hydrodynamic forces to be built up which tend to align the axis of the piston with that of the cylinder. These forces are countered by the biasing force of spring 28 which thus must continuously Contact the piston and exert a transverse force thereon to maintain the piston in a cocked position throughout its travel path.

It has been noted experimentally and through a computer analysis of the operation of the present dashpot timer that the time required for the piston to travel a predetermined distance within the cylinder varies exponentially in the manner illustrated in the graph of FIG. 3, with the angle 6, which the side of the piston makes with the side of the cylinder. The angle will, in turn, be determined by the length of the piston and the clearance between the piston and cylinder. Thus, in the referenced graph, e represents the percentage of cocked travel; that is, when e=l, the piston is fully cocked to the position shown in FIG. 1 and when e=0 the piston is resting against the side of the cylinder with side wall 18 of the piston abutting side wall 16 of the cylinder. The important point which this graph demonstrates is that when the piston is in a cocked position, the edge of the piston becomes extremely important. If that edge wears slightly, or if it is not uniform around the circumference of the piston, it may cause a slight change in the value of e and hence, may make a significant change in the time delay. Thus, a minute abrasion of the Teflon coat on the piston edge could effect the amount which the piston is cocked, and since the time curve is very nearly vertical as e approaches l and the piston approaches a fully cocked position, a slight change in the degree of cocking will have a significant change in the time delay. Consequently, care must be taken to assure that piston edges do not contain any sharp corners where the wear rate would be high.

In practice, it has been found that if the piston edges are beveled through a careful barrel finishing operation, a gradual curve 32 blending into a radius of about five thousandths to fifteen thousandths of an inch can be formed on the top and bottom peripheral edges of the piston, this effect can be essentially eliminated and the advantages of the increased time achieved by cocked travel are obtained. The curved ends are shown in greatly exaggerated form in FIG. 1.

With regard to the above, it has also been noted that if the cocking force, that is, the force exerted on the piston extension 26 by spring 28 is excessive, this could cause a high wear rate of the Teflon coating. The cocking force should therefore be just enough to overcome the hydrodynamic forces developed with some degree of safety and no greater. Anything in excess of this amount will create inconsistency problems due to abrasion of the Teflon film and to relatively high frictional forces between the piston edges and the cylinder wall.

For a better understanding of the present invention, an exemplary embodiment of an application thereof will now be discussed. Reference is now made to FIG. 4 wherein a rocket fuse 40 employing the dashpot timing device of the present invention is depicted. The fuse is utilized to prevent the possibility of detonation ofa rocket by holding the detonator out of line with the firing pin until the rocket has traveled a safe distance from the launching site and the rocket has attained a minimum acceleration. Accordingly, the rocket fuse 40 comprises an elongated housing 42 containing therein a fuse casing 44 having an open top end 46 and closed bottom end 48. A dashpot timer cylinder 50 in accordance with the present invention is disposed within the casing proximal the open end and constrained against movement collectively by the inwardly turning upper lip 52 of the casing and a guide member 54 which rests on the casing bottom and extends upwardly to the bottom of the cylinder. The timer further includes a piston 56 disposed within the cylinder 50. The piston 56 includes a cylindrical outer shell portion 58, the outer diameter of which is slightly less than the inner diameter of the cylinder and an inner shell portion 60 which is coupled to the inside of shell 58 and spaced inwardly therefrom. O-rings 62 and 64 seal the top and bottom ends respectively of the annular spacing between the inner and outer shells 60 and 58.

Both the cylinder and piston outer shell are formed of glass and the inner surface of the cylinder and outer surface of the piston shell are provided with a Teflon coating. The piston inner shell 60 has affixed to its forward end a protrusion 66 extending outwardly from the top end of the piston and through the open end 46 of casing 44. A transverse channel 68 is provided in the casing in line with the piston extension 66 which in turn is aligned with the longitudinal axis of the piston. A spring 70, initially compressed, is disposed within channel 68 as is a slider assembly 72. The spring and slider assembly extend between the fuse housing and the piston extension 66 and thus the spring exerts a force on the slider assembly 72 which in turn exerts a force on the piston extension tending to cock the piston relative to the longitudinal axis of the cylinder. A firing pin 74 is positioned in axial alignment with the piston extension and a detonator 76 is contained within the slider assembly 72. Thus, if the piston were shifted downwardly, the detonator would be urged, under the action of spring 70, to a position under the firing pin 74 whereafter detonation would occur when the rocket strikes its target.

The piston 56 is initially held against downward movement by a spring-loaded weight 78 which is initially urged upwardly against the bottom of the piston by spring 80. Another spring, 82, extending between a radially inwardly directed flange 84 disposed above the top of casing 44 and a shoulder 86 of piston 56, exerts a downward force on the piston. Spring 80 must, of course, be stronger than spring 82 to initially hold the piston in the position shown.

The operation of the fuse is as follows. The force exerted on spring 80 tending to compress the spring is equal to the mass of weight 78 multiplied by its acceleration. The spring and weight are chosen so that after the rocket has accelerated to some predetermined minimum g value, the necessary compressing force will be attained. Thus, when the desired acceleration is reached, weight 78 will shift downwardly away from the bottom of piston 56, leaving piston 56 free to shift downwardly. Spring 82 will then cooperate with the acceleration acting on the mass of the piston to urge the piston downwardly in the cylinder. During this time, the piston will be cocked and will remain in a cocked position through the action of slider 72 under the urging of spring 70. At a predetermined time after the desired minimum acceleration has been reached, piston 56 will have shifted downwardly a distance sufficiently to enable the slider 72 to clear the piston extension 66 and hence bring the detonator 76 in line with firing pin 74. This predetermined time will be determined by the stiffness of spring 82 as well as the geometry of piston 56 and cylinder 50. It should thus be noted that not until after the rocket has attained a predetermined acceleration will the piston 56 start to shift downwardly, and not until after a predetermined time interval determined by the characteristics ofthe dashpot timer, will the fuse become armed.

Thus, in accordance with the above, the several aforementioned objects are effectively attained.

Having thus described the invention what is claimed is:

1. A fuse for a projectile comprising: a housing; a dashpot timing means within the housing comprising a cylinder and a piston in said housing and adapted to move from a first position in the cylinder to a second position in the cylinder in a predetermined period of time, the piston having an extension extending outwardly of the cylinder; a weight means biased against the piston to hold the piston in said first position and adapted to be shifted away from the piston-holding position upon experiencing predetermined acceleration forces to thereby permit said piston to travel in said cylinder under the influence of said forces to the piston second position; a slider assembly biased against the piston extension; a detonator coupled to said slider, the piston extension holding the slider assembly in a retracted position when the piston is in the first position and when the piston is in the second position, the slider assembly being adapted to shift to an aligned position at which the detonator arms the fuse.

2. The invention in accordance with claim 1 wherein the fuse is adapted to be associated with a rocket projectile, said fuse having a firing pin, means mounting said firing pin on said housing such that the firing pin is adapted to be aligned with the detonator when the slider assembly is in the armed position whereby upon impact of the rocket projectile, the firing pin is adapted to strike the detonator to initiate the explosive train of the rocket projectile.

3. The invention in accordance with claim 1 wherein a coiled spring is biased against the piston for inducing movement of the piston within said cylinder together with the predetermined acceleration forces upon movement of the weight means from the piston-holding position.

4. The invention in accordance with claim 1 wherein the piston extension is in axial alignment with the longitudinal axis of the cylinder and when the piston is in the first position, the extension obstructs the movement of the slider assembly from its retracted position to its armed position and when the piston is in its second position, the piston extension clears the slider assembly so that the slider assembly is adapted to move to its armed position.

5. The invention in accordance with claim 4 wherein the slider assembly is biased against the piston extension to cock the piston relative to the cylinder by causing rotation of the longitudinal axis of the piston relative to the longitudinal axis of the cylinder.

6. The invention in accordance with claim 1 wherein the piston has an outer diameter slightly less than the diameter of the interior of the cylinder whereby a substantially annular orifice is defined between the piston and cylinder. 

1. A fuse for a projectile comprising: a housing; a dashpot timing means within the housing comprising a cylinder and a piston in said housing and adapted to move from a first position in the cylinder to a second position in the cylinder in a predetermined period of time, the piston having an extension extending outwardly of the cylinder; a weight means biased against the piston to hold the piston in said first position and adapted to be shifted away from the piston-holding position upon experiencing predetermined acceleration forces to thereby permit said piston to travel in said cylinder under the influence of said forces to the piston second position; a slider assembly biased against the piston extension; a detonator coupled to said slider, the piston extension holding the slider assembly in a retracted position when the piston is in the first position and when the piston is in the second position, the slider assembly being adapted to shift to an aligned position at which the detonator arms the fuse.
 2. The invention in accordance with claim 1 wherein the fuse is adapted to be associated with a rocket projectile, said fuse having a firing pin, means mounting said firing pin on said housing such that the firing pin is adapted to be aligned with the detonator when the slider assembly is in the armed position whereby upon impact of the rocket projectile, the firing pin is adapted to strike the detonator to initiate the explosive train of the rocket projectile.
 3. The invention in accordance with claim 1 wherein a coiled spring is biased against the piston for inducing movement of the piston within said cylinder together with the predetermined acceleration forces upon movement of the weight means from the piston-holding position.
 4. The invention in accordance with claim 1 wherein the piston extension is in axial alignment with the longitudinal axis of the cylinder and when the piston is in the first position, the extension obstructs the movement of the slider assembly from its retracted position to its armed position and when the piston is in its second position, the piston extension clears the slider assembly so that the slider assembly is adapted to move to its armed position.
 5. The invention in accordance with claim 4 wherein the slider assembly is biased against the piston extension to cock the piston relative to the cylinder by causing rotation of the longitudinal axis of the piston relative to the longitudinal axis of the cylinder.
 6. The invention in accordance with claim 1 wherein the piston has an outer diameter slightly less than the diameter of the interior of the cylinder whereby a substantially annular orifice is defined between the piston and cylinder. 